1) Field of the Invention
This invention relates to a laser welding head-controlling system, a laser welding head and a method for controlling a laser welding head.
2) Description of Related Art
A laser welding technique is suitable for fabricating an ultrahigh-vacuum apparatus composed of high precise processed parts made of a steel material. Recently, in the laser welding technique, a YAG (yttrium-aluminum-garnet) laser is widely used. The welding technique using the YAG laser has the following advantages: First, since the laser beam from the YAG laser is absorbed to parts to be welded of members to be welded made a metallic material effectively, the welding process can be carried out efficiently. Second, since the laser beam can be transmitted by an optical fiber, the laser welding head can be mounted on a three-dimensional welding apparatus or a steel-collar worker. Third, since a condenser and a laser beam-penetrating window can be made of quartz, they are safe at their destruction and can made in low cost.
On the other hand, the laser welding technique requires high precision in positioning the laser beam spot for realizing a high precise welding process. The latitude of the positioning operation is within 10% of the thickness of the members to be welded or 50% of the spot diameter of the laser beam. Since the spot diameter of the above laser beam is generally 1 mm or below in the welding process, the positioning precision of not more than 0.2 mm is required if the focused spot diameter is about 0.5 mm. Therefore, in this case, the welding laser head is controlled and traced along a welding line (seam line) so that the laser beam can be irradiated onto the parts to be welded at a precision of not more than 0.2 mm.
For realizing the above precise welding operation, parts constituting the laser welding head are made precisely, and positioning jigs and positioning sensors are mounted on the laser welding head.
However, the above conventional laser welding head becomes large in size and high in cost since it has the above complicate structure.
Moreover, a welding process using a CCD camera has been studied and suggested. In the welding process, the laser welding head is traced along a seam line on the monitored image by the CCD camera. However, as of now, the welding process is not generally employed because the CCD camera does not represent sufficient resolution.
In the case of joining the members to be welded densely, the space between the members becomes almost zero, so that the CCD camera can not detect the space as light and shade images. Moreover, since, for shortening the image processing period, an input image having 256 black and white gradations is needed, it may suffer from light reflection and flaws on the surfaces of the members to be welded made of a metallic material.
Although it is tried in many field to perform the welding process and the image processing at real time, the image processing is generally carried out prior to the welding process due to the slow image processing speed and the high welding process speed. That is, as of now, it is impossible to perform the welding process and the image processing at real time.
Moreover, since the welding process using the CCD camera requires a given space between the CCD camera and the members to be welded for monitoring the welding state of the members, the laser welding head having the CCD camera can not be downsized.